Low level asymmetrical transistor chopper



Jan 23, 1962 W. A. o,BERRY Low LEVEL ASYETRcAL TRANSSToR cHOPPER FiedJune 13, 1960 United SfateS Patent o 1 ne pfeSent invention felates fo atTanSiStor choppef and 111ofe paTticlllaTly to a tra1Sistof choppeT foTdeteI' ni11ing lov level difect cufTent outpnt changes.

In the use of paSSive cTyStal video TeceiveTS, it iS de Sifed toaccufately deteTn1i11e low level diTect cl1ffent oI1t pUt changes, atthe crySta1, due to feceived continuouS vvave energy. ModeTate inpl1tiInpedance of the ofdef of the detectoT cryStal dynan1ic inpedance iSdesifed vvith out adding dTift to tbe inpuf direct cUTTent leve1. It iSthese dTift conSideTationS that preclude the USe of an input cathodefonovVef. Also, low output iT1pedance iS de- SiTed Sice the inputiInpedance to the video aIIl olifiefS iS low.

In the pTeSent invention, a balanced Synn1etTical choppeT is pTovidedalong with a SyfnnetTica1 SquaTe wave chopping Signal. The diect cUTTentlevel to be chopped is Sn1oothed by a capacifor vhich pTovides a lowin1peda11ce SouTce fof a pulSe fofIning netWoTk. vVhen the SqIlaTe vavegoeS poSitive, the balanced Syn1InetTiCal choppeT is biaSSd on, and thepnlSe foIn1ing netwofk dischafgeS through a load iI1 a pulse. ZtTanSistor iS pTovided be tWeen the capacitor and the pUlSe formiognetWork, and dufing the application of the oSitive SquaTe vvave choppingsigna, thiS tTanSiStor is biaSed off thuS diScon- Ilecfing the ontputffom the direct cUTTent input. When the squaTe wave goeS negative andthe choppeT iS Switched off, the tTansiStor iS Swftched on and the pulSefofTning l1efvVoTk is chaTged ffonl the capacitof.

AII obiect of the pfeSent invention iS to pTovide n1eans foT chopping alow level diTect CUTTent output into video I)111Ses fo anovv the uSe ofeXiSting video anlp1ifS fof cononuons wave IneaSuTement.

()ther obiectS and adVantages of thiS invention vvill be readyappTeciated as the same becomes better undef- Stood by TefeTence to thefoHowing detailed descfiption vvhen conSidered in connection With theaccompanying draVving Whefein:

FIG. 1 is a Schenlatic TepTeSentation of one enbodi nent of the pTesenfinvention; and

FIG. 2 iS a gTaph ShoWing voltageS and time relations.

11efefTing now fo the dfaWing, and pafticIllaTly to FIG. 1, theTe isShown a balanced Syn1ITetTical choppeT 11 hav ing tTansiStoTS 12 and 13and tTansfofITler 14. TTanSiS tors 12 and 13 have the cuStomaTycollectof, eTniftef, and baSe electTodes, With the baSe electrodeS beingconnected to opposite endS of fhe SecondaTy Winding 15 of tranS fofInef14. The co11ectoTS of tTanSiSfoTS 12 and 13 afo connected to coIn1oI1point 16, vhich iS connected fo center-tap 17 of Secondafy vinding 15.Load 18 iS connected acrosS leads 21 and 22, as Shovvn, and a Sqllarevave c1opping signal iS applied to the pfinlaTy vinding 23 oftfanSforIT1ef 14 by 1eanS of leadS 21 and 24, vVbile Inany tTanSisforchoppeTS Suffef fToIn the effectS of TeSid11alvo1tage, or feedthToughvoltage, the voltages fToIT1 tfanSiStofs 12 and 13 tend t() cancel eachother and thus pToviding a IleaTly ideal 1ovv1eve1 choppef, on one haIfcyCle of the chopping ffequency, tTa11SiStof 13 is open and transistof12 is cSed, coInpleting the ciTcI1it ffon1 the inpnt thToUgh tTanSiStor12 and to load 18. ()n the a1teTnate half-oyclo, ffa11Sistof 12 is o enand franSiStof 13 is cloSed, effectively ShoTtciTcIiting the load 18.

The poSitive teTIina1 of a souTco of difect cnTTent 23 3,018,385Pofenfed Jan. 23, 1962 is connecfed to point 26, Which iS con1fnon togfonnd and lead 21, and the negative teTn1inal of difect curfent 25 fSconnected to lead 22 thfough TeSiStof 27. Capacitof 28 iS connectedacToss leadS 21 and 22. TranSistor 29 is connected in lead 22 With theeInitteT electTode being connected to con1n1on point 31 and theco11ectof electTode being connected to common point 32. The baSeelectfode of tfansiStof 29 iS connected to one end of the secondaTywioding 33 of ffanSfofn1eI' 34, With the othef end of winding 33 bei1gconnected to point 35, vvhich iS con1n1on to one lead of ca )acitof 28,The pfinaTy vvinding 36 of tfanSfoTn1ef 34 iS connected to the sqnafevvave chopping sigI1al. A pn1Se foTn1iI1g netWoIk 37, vve11-knovvn tothoSe SkiHed iI1 the aTt, is connected acroSS leads 21 and 22.

In operation, the difect C1TTent level, Which is SUpplied by SoUTce 25and iS fo be chopped, iS Smoothed by capaci toT 28, vvhich also pTovidesa low in1pedance soufce fof the pulse fofIning netWoTk 37. RefefTing nowto FIG. 2 of the dfaWing, Which Shovvs the inpoftant voltage and tiIneTelationS, it can be Seen that When the sqnaTe wave goeS positive, thechopper 11 iS biaSed o11 and the pulSe fofning fletvvofk dischaTgeSthTough the load 18 iI1 a pulSe. During thiS tiIne, tfansiStof 29 iSbiaSed o, thus diSconnecting the oI1tpI1t ffoIn the difect curTenfSouTce 25. vhe the SquaTe vvave goeS negative, chopper 11 is Switchedoff, tranSiStor 29 iS Svitched 011, and the pnlso fofn1ing netWork 37 iScharged ffom capacitof 28.

1f can thnS be Seen that the pfeSent invention pTovideS a nove1 IIlea11Sfor chopping a low level difect cllTTent ont 11f into video pnISeS toallow the 11Se of eXisting video aII1pli11eTs fof continuonS vvaven1eaSUTen1ent.

()bVioUSly Inany TnodicationS and vafiationS of the pTeSent invenfionaTe poSSible in the light of the above teachings. It iS theTefoTe to beundefSfood, that vvithin the Scope of the appended claiIns, theinvention Inay be pTacfced otheTWise than aS Specifically deScfibed.

what iS claimed iS= 1. A low level aSyn1Ifletfical tranSiStof choppefcon1 pTiSing= (Z) a sorce of difect cllfrent voItage to be chopped,

(Z)) a firSt tTanSistof having enittef, collectof and baSe electrodeS,

(C) a symmeffical choppef compfiSed of a pair of innction tTa1SiStoTS,each having en1itter, Collecfof and baSe electTodes, and a tfanSfoTInerhaving a pTi mafy and a SecondaTy Winding, said baSe electTodes of saidjunction transiStoTS being connected to diffeT- ent endS of saidSecondafy vinding,

d Said Tst tTanSistor and said S mnletTical cho er being connected i11Sefies vZith Said souTce,

(e) a soI1fce of SquaTe wave chopping vohage con nected to Said baseelectTode of Said fiTSt tfanSisfof and to said pfin1aTy vvinding of saidtTanSfoInlef,

( f) a p111se fofIning netvvork Shnnted acroSS Said difect cUTTentSouTce, and

(g) a neanS fof chafging said pulse fofo1iog netvork Whe Said choppeT isin an off coIldition.

Z. A lovv level aSynnnetrical tfaf1SiStoT chopper compfising:

(zZ) a Soufce of difect cuffent voltage to be chopped,

(Z7) a capacitOT ShUnted acroSS Said sonTce of diTect cuTTent voltage,

(c) a svvitching tra11SiStoT having en1ittef, CollectoT and baseelecffodes,

(Z) a syInInetTical chopper conlpfiSed of a paif of iUnctiontfanSiStoTS, each having eIT1itteT, collectof and base elecfTodes, and afiTSt tTa11SfofInef having a fifTlafy and a SecondaTy viI1ding, SaidbaSe e1ec tTodes of Said iunction transistofS being conected todi1fefent endS of Said secondafy Winding,

(e) said rSt tranSiSto1 and said SymInetTica1 choppeT being connected inSeTieS with said soufce,

() a second tfansformeT havi11g a pTinlary and a Sec ondaTy Winding,Said Secondary Winding of Said Second tTanSfoTmef having one endconnected to Said base electTode of Said SWitching tTaoSistof and theother end connected to a point con1n1on to one end of said capacitof,

(g) a SOUTce of sqnare vvave chopping voltage co11- nected to saidTin1ary vvindings of Said fiTSt and sec ond tTanSfofnleTS, and

(z) a pulSe foTming net vok shunted acroS Said di Tect cI11ent souTce.

3. A low level aSyInfnetrical tTanSistor choppef aS Set forth in claiIn1 wheTe Sad n1eanS foT chaTging Said pulSe f()rIning network conlpriSesa capacitor shunted acfoSS Said SouTce of diTect cuIent Voltage,

Refefences ced i1 the me of this patent UNITED STATES PATENTS

